import java.util.Scanner;

public class Main1 {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int count=0;
        double average=0;
        double sum=0;
        while(scan.hasNext()){
           int n= scan.nextInt();
           if(n<0){
               break;
           }else{
               sum=sum+n;
               count++;
           }
        }
        average=sum/count;
        //write your code here......
        

        System.out.println(String.format("%.2f",average));
        

    }
}